Project I: Normal human lamina propria lymphocyte manifest increased unstimulated apoptosis (when compared to peripheral lymphocytes) as well as enhanced apoptosis following stimulation via the CD2-activation pathway. This CD2 pathway-induced apoptosis downregulates cell expansion and cytokine production and thus protects the organisms from potentially harmful responses. In previous studies we demonstrated that lamina propria T cells from patients with Crohn's disease and ulcerative colitis manifest abnormal proliferation and cytokine production. It was therefore of interest to determine if such cells also exhibited abnormal patterns of apoptosis. We found that lamina propria lymphocytes of Crohn's disease patients showed defective CD2-pathway induced apoptosis. In addition, we showed that Crohn's disease lamina propria T cells although expressing comparable amount of cell surface Fas, are less sensitive to Fas-mediated apoptosis as compared to control cells. Finally, we demonstrated that Crohn?s disease lamina propria lymphocytes manifest increased expression of Bcl-2 following CD2-pathway stimulation and elevated Bcl-2 levels in cultures of unstimulated T cells. These studies thus establish that T cells in the inflamed lamina propria of Crohn's disease patients manifest decreased CD2-pathway-induced apoptosis and elevated Bcl-2 levels. These changes are likely to be secondary to the chronic inflammation and may aggravate disease in patients with IBD. Project II: Chronic intestinal inflammation in several animal models has been shown to be mediated by IL-12-driven Th1 T cells. These findings led us to evaluate IL-12 function and signaling in patients with inflammatory bowel diseases. In initial studies we showed that CD40L plus IFN-gamma-stimulated lamina propria (LP) macrophages from patients with Crohn's disease (CD) but not from patients with ulcerative colitis (UC) produce significantly higher levels of IL-12 p70 as compared to control macrophages. In further studies we demonstrated that CD4+ T cells from CD but not UC patients exhibit high levels of IL-12R Beta-2 chain and intranuclear STAT-4 expression. Finally, we showed that down-regulation of STAT-4 by an antisense oligonucleotide strikingly reduced CD4+ T cell IFN- gamma production in CD. In summary, the data suggest a critical role for IL-12 in the differential immunopathogenesis of CD and UC: whereas high levels of IL-12 in CD lead to generation of IFN-gamma-producing Th1 cells, low IL-12 levels in UC favors production of T cells producing Th2 type cytokines. Thus, activation of the IL-12/STAT-4 pathway emerges as a central mechanism in the pathogenesis of Crohn's disease that could be an attractive target for therapeutic intervention.